1. Field
The present invention relates to a route confirmation method and device for preliminarily confirming the state of a protection route selected.
2. Description of the Related Art
An example of a common router composing an IP network is shown in FIGS. 20 and 21.
FIG. 20 shows a functional block diagram of such a router as known in the art, in which this router is composed of interfaces IF#1-IF#n each serving as a gateway of subordinate networks NW#1-NW#n, a transmitter/receiver portion 2 for transferring data to/from those interfaces, a routing cache 3 that is a route memory area for routing packets to known routes or paths without intervention of softwares, and a routing table 4 for retrieving transfer destinations of packets.
An operation of this router is shown in FIG. 21. Packets inputted from the interfaces IF#1-IF#n are received by the transmitter/receiver portion 2 (steps S41, S42). When the destination address of a packet received has been already registered in the routing cache 3 (step S43), the packet is outputted to proper interfaces IF#1-IF#n through the transmitter/receiver portion 2 without intervention of softwares (step S45).
On the other hand, when a packet received has a destination address unregistered in the routing cache 3, a target route (interface) is retrieved from the routing table 4 with a software and the packet is outputted through the transmitter/receiver portion 2 (steps S44, S45).
An IP network provided with a plurality of such routers is usually designed to keep a communication between users by switching over to an operation in a protection route at the occurrence of a fault in a working route.
In this connection, there has been proposed a line switching system provided with a function of determining if a communication with an opposed side through a connection line is enabled and switchable, wherein a measured delay time of a connecting circuit is provided to a timer; the timer is given a switching signal based on a logical AND of a switching signal and a switchable signal and delays the switching signal as needed to be sent to a switching control device (See e.g. Japanese Patent Application Publication No. 63-3522).
Also, there has been proposed a line switching control method wherein a management table formed based on configuration information such as a transmission device and a line configuring a transmission network and on collected fault information such as input interruption and error rate deterioration is provided in a monitoring center; when an operator of the center makes switching instructions, it is determined whether or not a line disconnection occurs by referring to the management table, in which in the absence of line disconnection a switching control signal according to the switching instructions is provided while in the presence of line disconnection, the operator is notified to that effect, so that no switching control signal is provided (See e.g. Japanese Patent Application Publication No. 10-261981).
While it is recently generalized to provide a redundant structure across a plurality of networks as an IP network is speeded up and larger scaled, the number of devices composing the network is minimized for the cost reduction. Under such a circumstance, the following problems are mentioned:
<Problem 1>
Since it is not possible to determine whether or not a protection route can be communicated while a working route is being used, a switchover from the working route to the protection route in a state where a fault has occurred in the protection route would cause a disconnection state;
<Problem 2>
Since it is not possible to determine whether or not a data communication quality of a protection route is guaranteed while a working route is being used, a switchover from the working route to the protection route in a state where the communication quality of the protection route has eminently decreased for some reason would cause an eminent decrease of the communication quality in comparison with the state before the switchover;
<Problem 3>
Since it is not possible to determine whether or not a multicast stream can be received in a protection route while a working route is being used, a switchover from the working route to the protection route in a state where a fault has occurred or a multicast stream communication setting is not arranged in the protection route would disable the multicast stream to be received.